Electric-resistance furnace.



L. UBBELOHDE.

ELECTRIC RESISTANCE FURNACE. urmonmx PKILED D130. 22, 1911.

Patented May ,1913.

2 SHEETS-SHEET 1.

Witnauu- W Diva 4m Attorney.

L. UBBELOHDE.

ELECTRIC RESISTANCE FURNACE.

APPLIOATION FILED DEC. 22, 1911.

Patented May 6, 1913.

2 sums-sum 2.

Invent or I Witnaaseaillustrated two constructional forms of the LEO UBBELbHDE, OF KAELSBUHE, GERMANY.

Specification of Letters Patent. Application filed December 22 1911. Serial No. 867,856.

ELECTRIC-RESISTANCE FURNAGE.

Patented May 6, 1913.

To all whom it may concern Be it known that I, Lno Uannnorron, a subject of the German Emperor, residing at 41 Bismarcks'trasse, Karlsruhe, Baden, Ger- 5 many, have invented a certain new and useful Electric-Resistance Furnace, of which the following is a specification.

This invention relates, to an electric resistance furnace of the type in which metals which oxidize in air, are employed as the resistance. To prevent the in uriOus action of oxidation, it has been proposed, to exclude the oxy en of the air by surrounding the resistance hody by an air-tight substance, or to prevent oxidation by allowing free access to reducing gases, such as hydrogen.

According to the present invention, the oxidation is avoided by surrounding the metal, which is liable to oxidationby a orous electric insulator and then in the known manner, by a layer of carbon. A similar arrangement is already known, but it is for quite a different purpose to that-"of this invention. 25.

In the prior case the carbon does not act as a protecting agent but the oxidation of the electric resistance is avoided by the ad mission of a reducing gas, while the porous layer surrounding the resistance serves as a heat insulator andis adapted to prevent the carbonization of the resistance body. The invention is thus clearl seen in view of the difference of purpose .or which it is to be em loyed.

n the drawings are diagrammatically invention.

Figure l is a longitudinal section of one constructional form. Fig. 2 is a plan corresponding ther eto and Fig. 3 is a longitudinalsection ofa modification.

The resistance wire -a which consists of a metal liable to oxidation, is wound in spiral windings around a heating tube 6 composed for example of orcelain, glass or I the like, and is also embe ded in a covering 0 of a porous electric insulator, which latter is surrounded by a carbon layer d adapted to prevent oxidation. The whole is then inclosed in a metal casing e and .the ends of the metal casing are closed by asbestos sheets f, which are screwed into position, and connectedtogether by the electrical insulating material, for the purpose of preventing access of air. The sheets of asbestos are retained in position by a metal cap 9. As

[electric insulators such substances are employed which donot volatilize when exposed to theair or to high temperatures. v

A mixture of pulverized kaolin and alumina, fibrous asbestos and water glass, which mixture can be made plastic by the addition of small quantities of sodium carbonate, is very suitable for the purpose and ofl'ers the advantage that'itwill not burst.

The insulating intermediate layer is adapted for the purpose of preventing direct contact between the carbon and theresistance wire. The carbon 1n this instance 1s charcoal, which as is known, possesses the property that when in a pulverized condition it will not commence to conduct until a high tempera ture has been reached. It has been proved that at about 600 the pulverized charcoal becomes such a good conductor that a short circuitis formed and the wire burnt out at any point. In consequence of the porosity of the insulating layer, the'protectin action of the carbon is not afi'ected. I for example, there is any air between the carbon, this is burnt with the carbon, and forms carbonic acid and carbonic oxid corresponding to the relative value of the carbonic acid. This gas mixture forces its way through the pores of the insulating layer, and retains the resistance wire continually in a reduced condition. s

In order to insulate the electrical resistance wire from the carbon and simultaneously to protect it against the oxidizing action of the air, it is possible to employ a solid tube 0 of clay surrounded by carbon 'or a tube of carbon cl secured to the metal. casing, the tube 0 of clay bein of a some-T what larger internal diameter t an the wire winding a so that a free space 6 remains insuflicient, without having regard to thefact, that at such strength of current, the

I thin resistance wires fuse in the furnace, in consequence of being over heated at certain parts.

- it constant; The steadying resistances are 1 not only very expensive but consume elec- 'cient, for example, an iron alloy'containing spiral wire around said member, a layer of 'lar member a non-conducting member dissistance of about 46% higher than at 20 so that it is possible to startj heating up the fur- It is consequently necessary'when commencing theheatingup to employ high steadying resistances which as soon asa high temperature has been obtained are no longer necessary for controlling'this and retaining trical energy. This disadvantage is avoided if'alloys having a low temperature co-effiabout 25% nickel, is employed as the resistance wire, which at 1000 has only a renace at the full workingspotential thus avoiding all losses in energy. i What I claim as my invention anddesire to secure by Letters Patent is 4 ,1. In an electric furnace, the combination of a central tubular member said member consisting of a non-conducting substance, a

Carbon surrourlding thewireand the tubuosed between the tubular member and the. ayer of carbon, and a' metal casing surrounding-the layer of carbon. v

2. In an electric furnace the combination of a central tubular member said member consisting of a non-conducting substance, a spiral 'Wirearound said member, a layer of carbonv surrounding the wire and the tubular member, a porous insulator between the said wird and the layer of carbon, the spiralwire being embedded in said porous IIlSllr lator, and a metal oasing surrounding the layer of carbon. v

- 3. In an electric furnace, the combination of a central tubular. member, said member consisting of a non-conducting substance, of

spiral wire around said member, a layer of carbon surro'unding'the Wire and the tubular member, and a. metal casing surrounding the layer of carbon, a orous insulator between the tubular mem er and the layer of carbon surrounding the wire and the tubu lar member, a porous insulating member disposed between the central tubular member;

and the carbon layer consisting of a mixture of' asbestos, kaolin, alumina, and water-glass,

and a metal casing, surrounding the layer of carbon.

In testimony whereof I have hereunto signed my name to this specification in the presence at two subscribing Witnesses.

v LEO 'UBBELonnE.

v Witnesses: I

LUISE OFFENBURGEB,

A. VonnnRAUER. 

